A question was asked on the Locomotive Enthusiasts forum a while back, and hasn't so far been answered there. The MLW M420 (and apparently also its M424 variant for Mexico and the H412) had, as its traction alternator, a GTA-17, supplied by Canadian General Electric. Does anybody know what this is? CGE supplied GTA-9 and GTA-11 alternators for six-axle MLW units, so my guess is that this is something smaller and cheaper. (Not MUCH cheaper, since GE was happy to use the GTA-11 on AC/DC transmission U23B and B23-7!)
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Now a similar but slightly earlier case. U.S. built Alco switchers with six-cylinder 251 engines (S-6, T-6) had GT-584 traction generators. (This generator was also used on at least some Alco export locomotives with 6-251 engines: for example, the first series of New South Wales (Australia) Class 48 units (these locomotives were built in Australia with some imported components; later series substituted non-GE electricals).) But MLW-built switchers (and ??RS23?? light roadswitchers) with this engine got a GT-740. ... My initial suspicion was that this was the same thing as a GT-584 but with a different serial number, but since the GT-581 supplied for larger MLW power were called "GT-581" it doesn't appear that CGE gave different model from those used in the U.S.

Been trying to find out information on GE/AlCO class 90 (251 engine) locomotive excitation systems for GT 584 genny's. The units are used on the White Pass and Yukon. My guess is that they use the amplidyne system since the class first came out in the 1950's and amplidynes where GE's system of choice back then. I can't seem to find anything out. Because the units bridged several years I bet the units used at least a couple different systems. Did they start with amplidynes, move into the 3 field system, then the type E? Anybody work on these or similar units? Can anyone help?

I don't have my notes handy, but I did some research on main generators and excitation several years ago. IIRC, the S-5 and S-6, which were 8- and 900 HP with the 6-251, used split pole, just like the S-series switchers and the RS-1. I suspect the White Pass units were similar, from the same time period and with the same horsepower. I really don't remember what the T-6 had for excitation; and don't have any electrical drawings on file.

Split pole was fine for smaller units, but the larger ones, say 1500 HP and up, seemed to need something more sophisticated, hence the progression from amplidyne to simplified amplidyne, static, red card type E, blue card type E, and then three field, used by Alco only on the C-415.

Electricalwilly--Interesting question... to whichI have no answer! The first GE locomotives for the WP&Y with Alco 6-251 engines were built in 1954 (with engines from the same lot that provided the engines for the first S-5 switchers). Now, bigger locomotives didn't start being built with Static Excitation for another couple of years: Alco's 251-engined road switchers (Dl-701, Dl-600B) were introduced with static excitation-- the first were built in early 1956. MLW, which continued building the 244-engined RS-10 for a while after Alco shifted to the 251, switched to static excitation (hence the suffix letter in the designation "RS-10S" for later units of this type) in 1956. Fairbanks-Morse locomotives tarted getting GE static excitation electricals instead of amplidyne in 1956...

But, just as Alco sensibly tried out the 251 engine in small locomotives (S-5 switchers) before introducing the V-12 and V-16 versions of the engine on road locomotives, it would not be surprising if GE had tried out their static excitation technology "in miniature." While searching the WWWeb to see if I could find anything relevant to your question, I found a reference to a ten-page pamphlet (?) on Static Excitation locomotive control systems by a GE engineer... dated 1954!

So. It is possible that the WP&Y locomotives you ask about represent a key step in the development ofGE's locomotive technology: the "service test" units in the development of static excitation control! So I hope SOMEBODY can answer your question!

(I looked at the Kirkland and Steinbrenner books on Alco this afternoon: no definite statement on the matter, but wording suggesting that the 251 engine and static excitation were parallel, contemporaneous, developments. ... If I can broaden your question: what sort of control systems were used on S-5 and S-6 switchers?)

I have a couple of articles on the 1963 batch of WP&Y locomotives, or rather two variations on the same basic article. One is from ‘Diesel Railway Traction’ for 1963 October, and the other is from ‘Railway Gazette’ for 1963 November 15.

According to those articles, in these locomotives the Alco 6-251 engine was set to deliver 800 hp to the GT584 main generator. A belt-driven GMG-158 combined exciter-auxiliary generator was fitted. Nothing was said about “external” load control (Lemp 1914), but that does not mean it was not used. For example, the Alco DL-531 export locomotive also used the GT584 and GMG158 combination, and this did have external load control via an integral rheostat in the Woodward PG governor. On the other hand, GE did use inherent characteristic (Lemp 1924) load control in this power range, as in the 70-tonner and in the small Caterpillar-engined Universals. The WP&Y units could have been either way.